Marine propulsion and constructional details thereof

ABSTRACT

A fin for use on a propeller, the fin comprising a lift generating section having a leading edge and a trailing edge, and a pair of surfaces extending between the leading and the trailing edges thereby defining a tip and a root having a root chord; and a dihedral section integrally formed with the root of the lift generating section and having a rotation axis about which, in use, the lift generating system can be rotated to vary the dihedral of the fin, the axis being generally parallel to the root chord of the lift generating section.

BACKGROUND TO THE INVENTION

The present invention relates to marine propulsion systems and tomethods of providing controlled moments about the yaw, pitch and rollaxes of a craft independently whilst also providing controlled thrustforces in the axial and transverse senses. The invention also covers apropeller, a fin or blade for a marine propulsion systems and methods ofproviding dihedral control and folding, including mechanisms forcontrolling the pitch and dihedral (as defined below) of the fins on thepropellers.

Whilst the inventions have particular application to propellers forboats and ships, they will have application to other propellers andlift-generating rotors.

PURPOSE OF THE INVENTION

The various aspects of the invention have one or more of the followingprincipal objectives:

-   1. Hull Trim Control

The drag or resistance of high-speed hulls, and planing hulls inparticular is very dependent on the hull trim angle. The optimum trimangle is particularly dependent on craft surge speed and displacement.

In the case of stepless ‘V’ hulls in particular, but generally forhigh-speed hulls, the centre of lift moves aft as the speed increases.Whilst the use of some form of dynamic ballasting such as waterballasting, may be used to vary the centre of gravity position tocorrect for relatively slow variations in the centre of gravityposition, much faster response is required for effective craft trimmingwhilst accelerating or running in a seaway.

The first objective of the present invention is to provide effectiveforces and moments to enable effective static and dynamic craft trimmingby means of thrust vectoring with minimal change to propulsiveefficiency.

-   2. Turning

Turning a craft efficiently requires that the roll, trim and yaw anglesare established and maintained such as to optimise variables includinghull drag or resistance, side-slip, and ride comfort.

A second objective of the present invention is to provide effectivemeans of thrust vectoring to enable the roll, trim and yaw angles andrates of a craft to be independently set up and maintained such thatthese angles and angular rates may be optimised by a correspondingcontrol system without recourse to rudders, trim tabs or likedrag-creating control surfaces.

Optimisation of these variables results in minimal power loss in turns.

-   3. Improved docking & Low-speed control

Boats in general, but in particular lightweight planing craft show verypoor directional stability at low speeds and helm-reaction is slow.Maneuvering frequently requires operating the helm, clutching andthrottling one or more engines and operating a bow thruster.Furthermore, all drives other than controllable pitch propellers andwater jets have a minimum boat speed which is fixed by engine speed. Forfast craft this minimum speed may be 8 knots or even higher. Improvedgearboxes have recently become available TwinDisc U.S. Pat. No.4,186,829, U.S. Pat. No. 6,443,286, U.S. Pat. No. 6,666,312, CaterpillarU.S. Pat. No. 4,125,039 and Volvo Penta U.S. Pat. No. 5,992,599, ZFPatent No DE10035480. These rely on modulating the drive clutch andlargely remove the minimum speed limitation.

Docking and low speed manoeuvring in confined spaces requiresconsiderable tuition and practice and remains a time of high stress forpilots.

A third objective of the present invention is to enable low speed thrustvectoring such that the velocities and accelerations in the fore/aft,lateral and yaw directions may be independently controlled such as toenable dynamic positioning and simplified docking and low-speedmanoeuvres without declutching or gear changing or the use of complexcontrols.

-   4. Motion Control

A fourth objective of the present invention is to provide fast andefficient thrust vectoring to enable effective 6-dimensionalstabilisation for fast craft without the requirement for stabilisingfoils or other drag-producing control surfaces

-   5. Speed Range for High Propulsive Efficiency

A fifth objective is the provision of a propulsion system with very highpropulsive efficiency over a broad operating spectrum.

-   6. Fin Folding

A sixth objective is the provision of means for folding the blades ofsuch propulsion devices for the purposes of beaching or operating invery shallow water.

-   7. To Enable Individual Changing of Fins

When propellers are damaged due to striking logs or other debris,invariably only one or two blades are damaged. The ability to readilychange only damaged components can lead to a reduction in cost ofreplacement

-   8. To allow fins to be changed in the water-   9. To provide a streamlined root section of minimum cross section to    minimise churning losses at low craft speeds when the propeller is    largely immersed-   10. To provide a shape which allows large dihedral angles and    folding-   11. To allow for simple manufacturing and metrology in volume-   12. To minimise weight and optimise stress distribution-   13. To minimise control moments and allow for fail safe operation-   14. To provide a clean form which does not tend to trap logs and    other flotsam in order to reduce damage in case of log strikes.    System control variables are:    For dual propulsor installations:    Port Pitch, trim and engine speed    Starboard Pitch, trim and engine speed    With 5 variables to control, the speed of the two propulsors may be    kept the same    Alternatively, for single or dual propulsor installations:    Collective and Cyclical pitch    Collective and cyclical trim.    Engine speed

For dual propulsor installations this provides too many variables sothat cyclical controls could be used to optimise for non-axial incomingflow, etc.

It is only possible to control a marine vessel about 5 axes (Fore/aft,side/side, Roll, Pitch and Yaw). The sixth axis (Vertical) is notrequired as the craft is a surface craft, thus only 5 control variablesare required. Thus being able to control the pitch, dihedral (the term‘trim’ used in this specification is a marine term for trimming a driveto control the pitch attitude of a boat hull) of two propulsors and tocontrol a common engine speed is a sufficient number of variables. Inthe case of a single propeller, control of collective and cyclical pitchand dihedral and engine speed is required to achieve the required 5control variables.

In the above cases the word “trim” is taken to mean the means ofcreating forces to trim the craft, e. g. variable dihedral, variablerake, variable swash, or variable tilt.

Whilst aspects of this invention have application to fixed pitchpropellers, it may be more generally applied to controllable pitchpropellers which may be provided with collective pitch control or bothcollective and cyclical pitch control. Cyclical control may be a simplesinusoidal variation or some more complex motion involving higher-orderharmonics.

Whilst variable dihedral is the preferred mechanism, similar, if lessdesirous effects may be achieved by the use of controllable rake. Theconventional methods using variable tilt, or variable swash, are notsuitable due to the large variation in cyclical angle of incidence whichresults from the use of such mechanisms. This is discussed further inthe specific description of FIGS. 58 to 67.

Aspects of the invention further relate to methods of folding the bladesof such propulsion devices for the purposes of beaching or operating invery shallow water.

A craft to which devices including these new inventions are fitted willpreferentially be provided with a propulsion management system.

Rake: Rotation of a fin about an axis located in the root of the fin andwhich is in or parallel to the plane of rotation of the propeller hub

Dihedral: Rotation of a fin about an axis located in the root of thefin, irrespective of the orientation of the fin relative to the hub

It will be appreciated that the term dihedral angle is not generallyused in the definition of propellers. It will be defined by reference toFIG. 11 as the angle between the stack axis 320 and the pitch axis AA asit is rotated about axis BB. The stack axis has the same meaning as itsusage in the specification and manufacture of turbine blades and is theaxis along which sections used in the design and manufacture of suchblades are arranged. In the case where the pivot axis lies in a planenormal to the rotation axis of the propeller the dihedral angle will bethe same as the rake angle.

The invention enables the propulsion device to control all the motionsof the craft, namely: forward and reverse displacement, axial velocityand acceleration or braking; lateral displacement, velocity andacceleration; heave position, heave velocity and acceleration; rollangle, velocity and acceleration, pitch angle, velocity andacceleration, yaw (steering) angle, velocity and acceleration. Suchdevices as rudders, flaps, foils or stabilisers are not required forthese functions, although they may be used in conjunction with thepropulsive device of the current invention.

The propulsors of this invention may be used in conjunction with acontrol system to optimise the attitude of the craft to maximise itsspeed, acceleration, the general handling and steering of the craft, andits motions in roll, yaw or pitch. An independent aspect of thisinvention allows for the controlled use of water ballast to optimise thesteady-state trim (pitch angle) of the craft. Further aspects of thisinvention relate to docking a craft and to its operation in the case ofthe failure of a prime mover or a propulsor.

The propulsors of this invention may also be used in conjunction with acontrol system for the purposes of dynamic positioning, simplifieddocking and manoeuvring at low speeds, and for the navigation of thecraft.

Aspects of the invention are applicable to craft comprising a single ormultiple prime movers. The propulsion system may consist of a singlepropeller, a single or multiple pairs of contra-rotating propellers inwhich each pair of propellers rotates about a common axis, or dual ormultiple propellers rotating about parallel or individually orcollectively orientable axes.

Surface-piercing propellers are known to produce a great deal ofvibration due to the cyclical torque and thrust variation which can beas much as 100% of the mean value of either. Undertaking a Fouriertransform of the torque or thrust reaction forces indicates that themost energy is in the first and second fin orders, especially for 5 or 6fins

3 to 6 fins means that forcing frequencies will be present forsubstantial periods of time over the total frequency spectrum betweentypically 10 hz and 500 Hz

Rear mount deflect—keeping the fin roots within the shadow of the flowguides means that the deflection of the rear mount must be restricted.Conventional mounts require a deflection of up to 6 mm in order toachieve the required low frequency isolation, but a mounting having sucha characteristic would deflect excessively when subjected to the verymuch higher forces generated by a propulsion system designed to producethrust vectoring.

Heretofore, the reaction forces have largely been absorbed by thetransom of the craft. Vibratory forces reacted by the transom willgenerally result in considerable vibration being transmitted throughoutthe hull structure resulting in high levels of noise and vibration.

Marine propulsion systems to control yaw, axial thrust and side thrusthave been proposed by BUECHLER Dirk (EP1008514—Ship propulsion) andothers. Such devices have used controllable pitch and engine speed forthese purposes. However, the net side thrust achievable by this means ismodest under some conditions and reversing the side thrust directiononce motion has been established is difficult.

According to an aspect of the invention, there is provided a propellercomprising: a hub; and a plurality of fins extending radially outwardsfrom the hub, wherein each fin is moveably connected to hub such that,during rotation of the propeller, either the dihedral, the rake or boththe dihedral and the rake of the fin can be altered and controlled bymovement of the fin about one or more axes of rotation.

The propeller preferably further comprises a closed loop control systemto vary either the dihedral angle, the rake angle or both the dihedraland the rake angle of the fins during use.

The fin may be pivotable about a radial axis so as to control the pitchof the fin. The fin may be pivotable about an axis located in the planeof the rotational axis of the propeller. The fin may be pivotable aboutan axis generally parallel to the root chord of the fin.

The fins are preferably discretely moveable about at least one axisbetween at least two positions. The fins may be continuously moveableabout at least one axis between two positions.

The propeller may further comprise dihedral angle control means formoving the fins between the first and the second position. The dihedralangle control means is preferably arranged to vary the dihedral angle ofthe fins during use.

The propeller may comprise pitch control means for controlling the pitchof the fins. The pitch of the fins may be continuously variable. Thepitch control means may be arranged to vary the pitch of the fins duringoperation.

The propeller may be provided with means for varying the dihedral angleof one or more fins during one revolution of the propeller, such thatthe dihedral angle of any fin at top dead centre can be different to thedihedral angle of the fin at bottom dead centre, and similarly for thecross-axis.

The propeller may be provided with means to vary the pitch of one ormore fins during one revolution of the propeller, such that the pitch ofany fin at top dead centre can be different to the dihedral angle of thefin at bottom dead centre, and similarly for the cross-axis.

The closed loop control system may also vary the pitch of the finsduring use.

The propeller is preferably a surface-piercing propeller.

The range of dihedral angle is independent of the pitch angle.

The propeller may further comprise a master spline within the dihedralsection for, in use, aligning the fin in the desired orientation withrespect to a hub.

The centre of pressure of the fin is preferably located at a distance ofbetween 50% and 60% of the working surface span from the root section.

The centre of pressure of the fin is preferably located at a distance ofbetween 60% and 70% of the span from the dihedral axis.

The present invention also provides a boat having a hull and at leastone propeller as described above, wherein the hull is provided with afairing in front of the or each propeller and wherein fins are moveablesuch that they may be wholly positioned within the hull or the fairingprofile when viewed from the front.

The hub of the propeller may be contained wholly within the hull profilewhen viewed from the front.

The invention also provides a vehicle such as a water craft, ship,aircraft or helicopter having at least two propellers as describedabove, wherein at least one propeller is arranged to the starboard sideof the longitudinal axis of said vehicle and at least one propeller isarranged to the port side of the longitudinal axis of said vehicle.

Any propeller arranged to the starboard side of the longitudinal axis ofsaid vehicle preferably rotates in the opposite sense to any propellerarranged to the port side of the longitudinal axis of said vehicle.

Any propeller arranged to the starboard side of the longitudinal axis ofsaid vehicle preferably rotates in a clockwise sense when viewed fromthe rear and any propeller arranged to the port side of the longitudinalaxis of said vehicle rotates in a counter-clockwise sense when viewedfrom the rear.

The present invention also provides a craft comprising a hull and atleast one propeller as described above, wherein the control system isarranged to optimise at least one of the following: the trim angle andmotion of the craft by varying the dihedral angle of the fins of thepropeller(s); the roll motion of the craft by varying the dihedral angleof the fins of the propellers relative to each other; the roll motion ofthe craft by varying the dihedral angle of the fins of the propellersand their rotational speed relative to each other; the roll motion ofthe craft by varying the dihedral angle of the fins of the propellersand their pitch angle relative to each other; and the yaw motion of thecraft by varying the pitch of the fins of the propellers relative toeach other.

The propeller may comprise pitch control means in which the pitch meanscomprises two bearings disposed along the pitch axis of any fin in whicheither or both the first and the second bearings are angular contactbearings disposed such as to increase the effective centres of saidbearings.

The propeller may comprises pitch control means in which the pitch meanscomprises two bearings disposed along the pitch axis of any fin in whicheither or both the first and the second bearings are spherical bearingsdisposed such as to increase the effective centres of said bearings.

The pitch control means may rotate any fin about a spherical cup bywhich said fin is pivotally attached to the hub for dihedral anglecontrol.

The dihedral angle control means may comprise a lever arranged to exerta moment about the dihedral angle axis and which comprises a sphericalpivot at its inner end.

The dihedral angle control means may further comprise a link pivotallyattached to the inner end of the trim lever which is configured suchthat a first pivot of said link is aligned on the pitch axis when thecorresponding fin is arranged at its maximum design dihedral angle and asecond pivot is aligned on the pitch axis when said fin is arranged atits minimum design dihedral angle.

The shuttle is preferably configured to move in a substantially helicaltrajectory about the rotational axis of the propeller with suchtrajectory passing through, or at a proscribed distance from, the pitchaxis of the corresponding fin.

The trajectory of the fixing point of the link onto the shuttlepreferably bisects the angle of the link at the maximum forward pitchangle and the maximum reverse pitch angle, but it may be at some otherdesirable angle.

The pivot at the inner end of the dihedral angle lever is preferablyfree to slide in a radial direction in the shuttle. The shuttle may beconstrained to move along a helical trajectory.

The pitch angle is preferably arranged to be independent of the dihedralangle throughout its controlled range and is preferably arranged to beindependent of the dihedral angle throughout its desirable workingrange.

The pitch control moment range is prefer ably minimised.

Preferably, the pitch moment is arranged to be such that its directionis not changed during normal operation of the propeller.

One or more actuators are preferably provided to control each of thepitch and dihedral movement. These actuators may be arranged such thatthe actuators work together to control the dihedral movement and suchthat the actuators work differentially and/or independently to controlthe pitch movement.

The dihedral actuation may have a discontinuity between the normaloperating range and the folding range such that the pitch angle can beset to some optimum value prior to the folding operation.

The dihedral actuation may comprise a sector gear operating on the finholder.

According to an aspect of the invention, there is provided a fin for useon a propeller, the fin comprising: a lift generating section having aleading edge and a trailing edge, and a pair of surfaces extendingbetween the leading and the trailing edges thereby defining a tipsection and a root section; and a dihedral section connected to the rootsection of the lift generating section and having an axis about which,in use, the lift generating system can be rotated to vary the dihedralof the fin, the axis being generally parallel to the root section of thelift generating section.

The axis of rotation is preferably within a 15 degrees deviation fromthe root section, more preferably the axis of rotation deviates by nomore than 3 degrees from the root section. The axis of rotation may beparallel to the root section.

The dihedral section may comprise a front boss adjacent the leading edgeand a rear boss adjacent the trailing edge. Each boss is preferablyprovided with a through hole which is splined for engagement with acorresponding spline on a shaft in use. The axis of rotation preferablypasses through the centres of the through holes in each boss.

The front boss may advantageously blend smoothly into the leading edgesuch that no re-entrant is formed between the boss and the leading edge.

The fin may have a pitch axis and a stack axis and the pitch axis ispreferably closer than the stack axis to the leading edge. The stackaxis preferably does not pass through the axis of rotation. The stackaxis may be angled relative to the pitch axis. The centre of pressure ofa fin may be located forward of the pitch axis.

The fin may further comprise a stop element mounted on either or both ofthe front and rear bosses for limiting rotation of the fin about theaxis of rotation in at least one direction.

The fin may be provided with a surface between the front and rear bossesat the root of the fin shaped such that, when the fin is mounted on ayoke, the surface at the root of the fin acts, during rotation, toremove marine growth, sediment or other unwanted material from the yoke.

According to an aspect of the invention, there is provided a modularpropeller system having: a plurality of substantially identical finassemblies; and a plurality of hubs, each hub being arranged to receivea different number of the substantially identical fin assemblies;wherein a propeller of the desired number of fins can be created by theselection of the appropriate hub and the required number of thesubstantially identical fin assemblies.

Each fin assembly may include a fin having a lift generating surface anda leading and a trailing edge.

Each fin assembly preferably comprises a turret on which the fin ismounted, the turret being arranged to be connected, in use, to anengagement means in one of the hubs.

Each fin assembly may be connected directly to the hub.

Each hub may be provided with a plurality of engagement means, eachengagement means being associated with a respective fin assembly. Eachengagement means on each hub of the plurality of hubs is preferablyidentical.

Each hub may be formed from two cooperating sections and the twosections are, when constructed, preferably aligned along the rotationalaxis of the propeller.

The hub sections may be provided with cooperating recesses which, whenthe sections are aligned, define the desired number of receivinglocations for the plurality of fin assemblies.

The invention also provides a hub for a marine propeller, the hub beingformed from two cooperating sections which, when forming the hub, arealigned along the rotational axis of the hub.

The two cooperating sections preferably define a plurality of recessesinto each of which a fin assembly can be inserted, thereby forming apropeller.

According to an aspect of the present invention there is provided amount for supporting part of a marine drive system to a marine hull, themount comprising:

a rigid outer housing defining a radially outer circumferential surfaceon its radially inner surface;

a resilient mounting disposed radially with in the outer housing anddefining a radially inner circumferential surface, the marine drivesystem passing through and supported by the resilient mounting in use;

wherein a circumferential radial gap is provided either between theresilient mounting and the rigid outer housing or within the resilientmounting.

The rigid outer housing may be substantially annular.

The rigid outer housing may be circular.

The rigid outer housing may have an eccentric form.

The resilient mounting may be substantially annular.

The resilient mounting may be circular.

The resilient mounting may have an eccentric form.

Preferably, upon operation of the marine drive system the marine drivesystem radially deflects an arcuate portion of the resilient mountinginto a corresponding arcuate portion of the gap.

Preferably, wherein the gap is dimensioned such that the rate of forceproduced by the marine drive system to the radial deflection of themarine drive system is substantially linear.

Preferably, the gap is dimensioned such that the highest solid-bodyresonant frequency of the marine drive system is less than 1/√{squareroot over (2)} times the lowest forcing frequency generated by themarine drive system.

Preferably, upon operation of the marine drive system the marine drivesystem deflects an arcuate portion of the resilient mounting into acorresponding arcuate portion of the gap and compresses the arcuateportion of the resilient mounting against the rigid outer housing.

Preferably, the gap is dimensioned and the resilient mounting is formedsuch that the rate of force produced by the marine drive system to theradial deflection of the marine drive system increases progressively.

Preferably, the resilient mounting is formed from a micro-cellularpolyurethane material.

Preferably, the circumferential radial gap is an air gap and is providedover an axial length of the resilient mounting. The remaining axiallength of the resilient mounting is compressed, in use, such that itforms a seal between the outer circumferential surface and the innercircumferential surface.

A marine craft may be provided having a hull and a transom positioned atthe rear of the craft, the craft comprising a marine drive systemattached to the transom by means of the mount described above.

According to the present invention there is provided a mount forsupporting part of a marine drive system on a marine hull, the mountcomprising:

an annular resilient member having radially spaced inner and outercircumferential surfaces, wherein an annular groove forming an air gapis provided between the inner and outer circumferential surfaces.

According to the present invention there is provided a marine drivesystem comprising:

an engine connected to a gearbox by means of a drive shaft;

a propeller connected to the gearbox by means of a propeller shaft;

wherein the gearbox and the propeller are formed as a single rigid bodyfor mounting in the hull of a marine craft as a single unit; and

wherein the engine, gearbox and propeller are positioned such that theyare generally aligned with the longitudinal axis of the craft.

The gearbox may be disposed remotely from the engine and a rigid frameis connected between the gearbox and the craft.

The drive shaft may be formed from carbon fibre.

The single rigid body may comprise the engine, gearbox and propeller formounting in the hull of a marine craft as a single unit.

The engine and the gearbox may be positioned adjacent to each other.

Preferably, the engine, gearbox and propeller are aligned along thelongitudinal axis of the craft.

The marine drive system may further comprise a second propellerconnected to the gearbox by means of a second propeller shaft, theengine and the gearbox being aligned along the longitudinal axis of thecraft and the propellers being aligned with the longitudinal axis of thecraft.

The marine drive system may further comprise a second single rigid body;and

wherein each single rigid body is generally aligned with thelongitudinal axis of the craft.

Preferably, the ratio of the propeller diameter to the propeller shaftdiameter is in the range of 4.5 to 5.5

Preferably, the ratio of the propeller shaft diameter to the propellershaft length is in the range of 0.65 to 0.9.

Preferably, the gearbox has an input shaft driven by the engine and theratio of the propeller shaft diameter to the input shaft diameter is inthe range of 2.2 to 3.5.

Preferably, the ratio of the input shaft diameter to the input shaftlength is in the range of 0.5 to 0.62.

Preferably, the single unit is provided with front mounting pointsadjacent to the engine and rear mounting points adjacent to the gearbox,for attaching to the hull of the marine craft,

the rear mounting points being positioned at 8% to 12% of the overalllength of the marine drive system from the centre of the propeller; and

the front mounting points being positioned at 40% to 60% of the overalllength of the marine drive system from the rear mounts.

A marine craft may be provided having a hull and a transom, the marinecraft comprising a marine drive system according to any one of thepreceding claims;

wherein the marine drive system is flexibly mounted to the hull of themarine craft.

According to an aspect of the present invention there is provided amarine drive system comprising:

an engine connected to a gearbox by means of a drive shaft;

a propeller connected to the gearbox by means of a propeller shaft;

wherein the engine, gearbox and propeller are formed as a single rigidbody for mounting in the hull of a marine craft as a single unit; and

wherein the engine, gearbox and propeller are positioned such that theyare generally aligned with the longitudinal axis of the craft.

Preferably, the rotational axes of the drive shaft, the propeller shaftand the propeller are generally aligned with the longitudinal axis ofthe craft.

According to the present invention there is provided a propulsionassembly comprising:

a hub;

a plurality of fins moveably connected to the hub such that the pitchangle of each fin can be controlled;

a pitch shuttle moveable, by means of a pitch actuator, along an axiscoaxial with the axis of the hub;

a plurality of pitch linkages each connecting the pitch shuttle with oneof the fins arranged such that upon movement of the pitch shuttle, thepitch angle of each fin is varied.

Preferably the propulsion assembly further comprises means forcontrolling the dihedral angle of each fin.

Preferably the means for controlling the dihedral angle of each fincomprises:

a dihedral shuttle moveable, by means of a dihedral actuator, along anaxis coaxial with the axis of the hub;

a plurality of dihedral linkages each connecting the dihedral shuttlewith one of the fins arranged such that upon movement of the dihedralshuttle, the dihedral angle of each fin is varied.

According to the present invention there is provided a propulsionassembly comprising:

a hub;

a plurality of fins moveably connected to the hub such the dihedralangle of each fin can be controlled;

a dihedral shuttle moveable, by means of a dihedral actuator, along anaxis coaxial with the axis of the hub;

a plurality of dihedral linkages each connecting the dihedral shuttlewith one of the fins arranged such that upon movement of the dihedralshuttle, the dihedral angle of each fin is varied.

Preferably the propulsion assembly further comprises means forcontrolling the pitch angle of each fin.

Preferably the means for controlling the pitch angle of each fincomprises: a pitch shuttle moveable, by means of a pitch actuator, alongan axis coaxial with the axis of the hub;

a plurality of pitch linkages each connecting the pitch shuttle with oneof the fins arranged such that upon movement of the pitch shuttle, thepitch angle of each fin is varied.

Preferably each of the dihedral linkages has a first end which isspherically pivoted to the dihedral shuttle; and

a plurality of swing links are provided at the point of connection ofeach dihedral linkage to the dihedral shuttle;

each swing link having a first end spherically pivoted to the dihedralshuttle and a second end spherically pivoted to a point on the hub.

Preferably each swing link is arranged such that upon movement of thedihedral shuttle along the axis coaxial with the axis of the hub, thedihedral shuttle is caused to rotate around the axis coaxial with theaxis of the hub in a helical manner.

Preferably the pitch angle and the dihedral angle can be independentlyvaried.

A plurality of dihedral levers may be provided, each connecting one ofthe fins with a second end of one of the dihedral linkages, eachdihedral lever having an inner end which is spherically pivoted to thesecond end of one of the dihedral linkages.

Preferably the dihedral levers and the dihedral linkages are configuredsuch that the first end of each dihedral linkage is coaxial with thepitch axis when the fin is at a minimum design dihedral angle, duringoperation of the propulsion assembly.

Preferably the dihedral levers and the dihedral linkages are configuredsuch that the second end of each dihedral linkage is coaxial with thepitch axis when the fin is at a maximum design dihedral angle, duringoperation of the propulsion assembly.

The propulsion assembly may further comprise two bearings disposed alongthe pitch axis of each fin and either or both of the bearings areangular contact bearings disposed such as to increase the effectivecentres of said bearings or either or both of the bearings are sphericalbearings disposed such as to increase the effective centres of saidbearings.

Embodiments of the various inventions will now be described withreference to the accompanying drawings, in which:

FIG. 1 Propulsor comprising 6 fins arranged for controllable pitch anddihedral

FIG. 2 Isometric view of a propulsor fin arranged for controllable pitchand dihedral

FIG. 3 End view of a propulsor fin arranged for controllable pitch anddihedral

FIG. 4 Side view of a propulsor fin arranged for controllable pitch anddihedral

FIG. 5 Top view of a propulsor fin arranged for controllable pitch anddihedral

FIG. 6 Sectional view of a propulsor fin arranged for controllable pitchand dihedral

FIG. 7 Side view of a propulsor fin arranged for controllable pitch anddihedral with positive or negative skew.

FIG. 8 Isometric view of a fin assembly mounted to a hub

FIG. 9 Isometric view of a fin assembly mounted to a hub

FIG. 10 Detail section transverse view of a fin turret assembly withoutfin

FIG. 11 Detail section transverse view of a fin turret assembly with afin attached

FIG. 12 Detail cross-section of a turret assembly with fin, togetherwith bearing arrangements

FIG. 13 Detail cross-section of a turret bearing assembly

FIG. 14 Detail of pitch mechanism

FIG. 15 Detail of the pitch and dihedral mechanism from inside the hubwith 90 degrees pitch and 0 degrees of dihedral

FIG. 16 Detail of the pitch and dihedral mechanism from inside the hubwith 90 degrees pitch and 45 degrees of dihedral

FIG. 17 Detail of the pitch and dihedral mechanism from inside the hubwith 90 degrees pitch and the fin folded

FIG. 18 Detail of the pitch and dihedral mechanism from inside the hubwith 40 degrees pitch and 0 degrees of dihedral

FIG. 19 Force diagram

FIG. 20 Rectangular Envelope for Pitch and Dihedral

FIG. 21 Detail of the pitch and dihedral mechanism from the side. Pitchset to 90 degrees with the fin folded

FIG. 22 Detail of the pitch and dihedral mechanism from the side. Pitchset to 90 degrees and 45 degrees of dihedral

FIG. 23 Detail of the pitch and dihedral mechanism from the side. Pitchset to 90 degrees and 0 degrees of dihedral

FIG. 24 Detail of the pitch and dihedral mechanism from inside the hubwith 40 degrees pitch and 45 degrees of dihedral

FIG. 25 Isometric view of the pitch and dihedral mechanism from insidethe hub with 40 degrees pitch and 45 degrees of dihedral

FIG. 26 Isometric view of a modular hub without fins—exploded view

FIG. 27 Isometric view of a modular hub with one fin assembly inposition

FIG. 28 Side view of a modular hub with one fin assembly and pitch anddihedral shuttles in position

FIG. 29 Isometric view of a modular hub with four fin assemblies inposition

FIG. 30 Isometric view of a modular hub with four fin assemblies folded

FIG. 31 Isometric view—Propulsor Hubs in Flow Guide Cavity—HubsNon-Solid of Revolution

FIG. 32 Rear view of a modular hub with six fin assemblies in position

FIG. 33 Side view of a modular hub with six fin assemblies in position

FIG. 34 Rear view of a modular hub showing bolting pattern to propellershaft

FIG. 35 Rear view of propeller shaft

FIG. 36 Rear of a raked propeller

FIG. 37 Isometric view of a raked propeller

FIG. 38 Rear view of an un-raked propeller

FIG. 39 Isometric view of an un-raked propeller

FIG. 40 Rear view of a propeller with dihedral

FIG. 41 Isometric view of a propeller with dihedral

FIG. 42 Rear view of a propeller with zero dihedral

FIG. 43 Isometric view of a propeller with zero dihedral

FIG. 44 Rear view of a propeller with zero swash

FIG. 45 Isometric view of a propeller with zero swash

FIG. 46 Rear view of a swashed propeller

FIG. 47 Isometric view of a swashed propeller

FIG. 48 Side view of a swashed propeller

FIG. 49 Rear view of an un-tilted propeller

FIG. 50 Isometric view of an un-tilted propeller

FIG. 51 Rear view of a tilted propeller

FIG. 52 Isometric view of a tilted propeller

FIG. 53 Side view of a tilted propeller

FIG. 54 Control schematic for pitch and engine speed

FIG. 55 Control schematic for dihedral

FIG. 56 Control schematic for dihedral with IMU/INS input

FIG. 57 Propulsion mounting arrangement, dual engine

FIG. 58 Propulsion mounting arrangement, single engine

FIG. 59 Typical load-deflection curve, rear mount

FIG. 60 Sectional view through a rear mount

FIG. 61 Detail sectional view through a rear mount

FIG. 62 Sectional view through an alternative rear mount

FIG. 63 Engine & Propulsion unit with typical deflection curve forlowest bending frequency (vertical)

FIG. 64 Engine & Propulsion unit with typical deflection curve forlowest bending frequency (horizontal)

FIG. 65 Propulsion unit with separately mounted engine with typicaldeflection curve for lowest bending frequency (vertical)

FIG. 66 Typical cyclical thrust and torque variation for a 5-bladedpropulsor

FIG. 67 Fourier Analysis of cyclical thrust

FIG. 68 Simplified cyclical thrust force

FIG. 69 Typical 6^(th) and 12^(th) order transmission factors

FIG. 70 Typical mounting transmission factor

FIG. 71 Typical combined transmission factor

FIG. 72 Drivetrain arrangement

FIG. 73 Isometric view of the underside of a hull with a flow guide andpropeller

FIG. 74 Rear view of a hull with a flow guide and propeller

FIG. 75 Single engine power train

FIG. 76 Turret assembly arranged for rake

FIG. 77 Propeller arranged for cyclical pitch, rake and dihedral

FIG. 78 Detail of propeller arranged for cyclical pitch, rake anddihedral

FIG. 79 Isometric view of propeller arranged for cyclical pitch, rakeand dihedral

FIG. 80 Isometric detail of propeller arranged for cyclical pitch, rakeand dihedral

FIG. 81 Side view of propeller arranged for cyclical pitch, rake anddihedral

FIG. 82 Lift drag curve for high-efficiency ventilating sections

FIG. 83 Lift coefficient curve for high-efficiency ventilating sections

SPECIFIC DESCRIPTION FIG. 1

A propulsor 1 is arranged to rotate about axis CC and comprises a hub101 and six fins 3 each mounted to a turret 20 arranged for independentpivotal motion about a pitch axis AA and a dihedral axis BB. Axis AA isgenerally normal to the propeller axis CC. Axis BB is generally arrangedat 90 degrees to axis AA.

Fin 3 comprises a stop 316 which reacts against a planar area of yoke21.

FIG. 2

A propulsor fin 3 comprises a lift generating section 30 and a rootsection 31.

The lift generating section comprises a normally wetted surface 301, aleading edge 302, a trailing edge 303 and a normally un-wetted surface304.

The normally un-wetted surface is vented to atmospheric pressure duringnormal forward thrust conditions. During reverse-thrust conditionssurface 304 may become fully wetted and surface 301 may become fullyun-wetted. Under intermediate conditions either surface may be partiallywetted.

The root section (also referred to as “dihedral section” as it is thesection that allows the dihedral to be altered) blends smoothly into thenormally wetted and normally un-wetted section along two lines 305. Theroot section is un-wetted during normal operation but becomes partiallyor fully wetted at low speeds.

The root section has a generally smooth profile which may be a surfaceof revolution about an axis BB and comprises a leading edge boss 314, atrailing edge boss 313 and a bridge section 310. The leading andtrailing edge bosses comprise a common spline profile 315 preferentiallyhaving a master spline 3151 (see FIG. 3).

The trailing edge boss 313 comprises an inner face 3131 and an outerface 3133 (see FIG. 4) which are normal to axis BB. A lead in 3132 isprovided at the bottom of the inner face 3131. The trailing edge boss313 also comprises a stop 316 on the normally un-wetted side of fin 3.This stop reacts against a corresponding surface on the yoke 21 (seeFIG. 1)

The leading edge boss 314 comprises an inner face 3141 (see FIG. 4) andan outer face 3143 which are normal to axis BB. A lead in 3142 isprovided at the bottom of the inner face 3131. The outer profile 3145 ofthe leading edge boss is arranged to achieve a minimum wall thicknessaround the splined centre consistent with maintaining adequate fatiguelife and a smooth hydrodynamic shape.

A root section of fin 3 is angled at a small angle θ_(R) to axis BB. Atip section of fin 3 is angled at a larger angle θ_(T) to axis BB. Theangles θ_(R) and θ_(T) are preferentially disposed on the same side ofaxis BB, but may be disposed on different sides of said axis. The twistof the fin is defined by the expression

Twist=θ_(T)−θ_(R)

Wherein the twist is normally below 20 degrees and preferentially in therange 12 degrees to 16 degrees.

Propeller blades and other such lifting surfaces have traditionally beenmade by stacking a number of discrete sections together along a commonaxis and then fairing the complete surface. Even though the use ofnumerically controlled machines has largely replaced this practice theconcept of the use of a “stacking axis” is still in common use.

FIG. 3

The stacking axis 320 is shown having an offset 3202 from axis BB andinclined at an angle 3203 relative to the pitch axis AA. Such an offsetmay be used to reduce the centripetal moment exerted by fin 3 about axisBB when the fin is in its normal range of dihedral angle inclinedanticlockwise about axis BB by 5 degrees to 35 degrees. The trailingedge thickness 324 reduces from 3242 at the root to 3241 (see FIG. 2) atthe tip.

The outer profile 3135 of the trailing edge boss is arranged to achievea minimum wall thickness around the splined centre consistent withmaintaining adequate fatigue life and a smooth hydrodynamic shape.

FIG. 4

The stacking axis 320 is shown arranged at a distance 3201 be hind thepitch axis AA such that the fin centre of pressure 325 is at a distance3251 forward of the pitch axis AA. It will be appreciated that thecentre of pressure position will vary during operation, but that thecontrol moment about the pitch axis should be kept low in order to limitthe size of the pitch control mechanism. By keeping the centre ofpressure in front of the pitch axis as depicted any failure of the pitchmechanism will normally ensure that the fin rotates to its maximumforward pitch position.

The centre of pressure 325 is shown at a distance 3252 from the dihedralaxis BB. The dihedral control moment is governed by this distance and itwill be appreciated by those skilled in the Art that this distance isvery small in comparison with other methods of thrust vectoring.

The fin has a root chord 3222 and a tip chord 3221. The root chord isshown as being identical to the length of the root section formanufacturing simplicity and compactness, but it will be realised thatthe root section could extend forward and/or rearwards relative to theroot chord.

A key feature of the present invention is the ability to create a familyof fins from a single forging. The fin is shown with a span 321, but thesame forging may conveniently be cut down to trip profiles indicated by3061 and 3062 having spans 3211 and 3212 respectively.

The trailing edge root section 313 has an outer plane face 3133 and aninner plane face 3131 both arranged to be normal to the dihedral axisBB, and is arranged with a width 3134.

The leading edge root section 314 (FIG. 2) has an outer plane face 3143and an inner plane face 3141 both arranged to be normal to the dihedralaxis BB, and is arranged with a width 3144.

The root bridge section 310 is arranged with a profile of varying radius3102 swept about axis BB. The swept bridge profile is blended into theinner faces 3131 and 3141 with blending surfaces 3103, 3104.

The inner surfaces 3132, 3142 of root bosses 313, 314 are arranged withsurfaces finished for dynamic face seals. The outer surfaces 3133, 3143are finished for static seals.

FIG. 5

The top view shows the relationship between θ_(T) and θ_(R).

FIG. 6

FIG. 6 shows a part section CC derived from FIG. 5 with a detail of thepreferred profile for the bridge section. Two edges 311 are arrangedwith radial flanks to remove any marine growth from the arcuate surface317 of the mating component. The Internal profiles 3111 are arrangedwith a positive angle Φ to the surface normal to ensure that crustaceansand other debris does not jam. An alternative option uses an arcauteprofile between the tangent points.

FIG. 7

Whereas the preferred embodiment has a trailing edge normal to thedihedral axis BB to simplify manufacture and metrology, the trailingedge may be skewed positively or negatively through angle ψ as desired.

A removable fin according to this invention may beneficially havedimensions within the ranges shown in the table below:

Feature Min Max Key parameter Maximum span 100.00% Reduced span 75.87%100.00% Max working 77.23% 82.73% Of actual span surface span from tipRoot chord 50.00% 70.00% Of max span Tip chord 35.00% 48.00% Of max spanAverage chord 45.00% 65.00% Of max span Spline/shaft diameter 14.00%17.50% Of max span Tip trailing edge 6.00% 8.00% Of tip chord thicknessRoot trailing edge 9.00% 13.00% Of root chord thickness Average trailingedge 7.00% 10.00% Of average chord thickness Root cut-out width 50.00%65.00% Of root chord Trailing edge boss width 25.00% 21.00% Of rootchord Leading edge boss width 16.00% 20.00% Of root chord Centre ofPressure 50.00% 60.00% Of working position relative surface span to theroot section Centre of Pressure 60.00% 70.00% Of span from positionrelative dihedral axis to the dihedral axis Stack axis offset - 0.00%10.00% Of root chord dihedral axis

FIG. 8

A propulsor 1 is shown with a single fin 3 mounted by a retaining pinassembly 35 to a turret 20. Turret 20 is fixed to a hub 101 arranged fora plurality of fins. Turret 20 is arranged such that movement of a pitchpivot pin 211 results in rotation of the turret assembly and itsattached fin about axis AA, and movement of a dihedral lever 241 resultsin rotation of the fin about axis BB.

FIG. 9

FIG. 9 shows an external view of propulsor 1 with a single fin 3 mountedby a retaining pin assembly 35 to a turret 20. Turret 20 comprises ayoke 21 of generally ellipsoidal upper section.

FIG. 10

FIG. 10 shows a sectional view of a turret 20 without a fin 3 (FIG. 9)or retaining pin assembly 35 (FIG. 9) fitted. Turret 20 comprises a yoke21 of generally ellipsoidal upper section having a transverse bore inwhich a fin carrier 221 is arranged to pivot. Fin carrier 221 ispreferentially arranged with external splines 2211 of a central sectionand internal splines 2212 which may extend over its entire length.Internal spline 2212 preferentially comprises a master spline (notshown) for Poka Yoke assembly. External spline 2211 may also comprise amaster spline.

A dihedral lever 241 is fitted to the external splines and may be lockedin place by one or more grub screws 245 reacting against a thinned downsection of the lever. Thrust washers 227 either side of the dihedrallever react side thrust from lever 241 against internal flanks in thebore of yoke 21. Journal bearings 226 react forces from the fin anddihedral lever into yoke 21. Seals 223 maintain a seal between theinternal bore of yoke 21 and the external surfaces of fin carrier 221and also seal against the internal faces (not shown) of fin 3 (notshown). A four-point, bearing and seal cartridge 25 retains the turretassembly 21 in the propeller hub 101 and is sufficiently dimensioned totake the radial, axial and tilting loads imposed by fin 3 and dihedrallever without brinelling under the continuous load fluctuation exertedby fin 3 (FIG. 9).

A dihedral link, 131 comprising a high-capacity plain spherical bearing132 is retained to the inner end of dihedral lever 241 by screw 133.

FIG. 11

FIG. 11 shows a sectional view of a turret 20 with a fin 3 and retainingpin assembly 35 fitted. Turret 20 comprises a yoke 21 of generallyellipsoidal upper section having a transverse bore in which a fincarrier 221 is arranged to pivot. Fin carrier 221 is preferentiallyarranged with external splines 2211 (FIG. 10) of a central section andinternal splines 2212 (FIG. 10) which may extend over its entire length.Internal spline 2212 preferentially comprises a master spline (notshown) for Poka Yoke assembly. External spline 2211 may also comprise amaster spline.

A dihedral lever 241 is fitted to the external splines and may be lockedin place by one or more grub screws 245 reacting against a thinned downsection of the lever. Thrust washers 227 either side of the dihedrallever react side thrust from lever 241 against internal flanks in thebore of yoke 21. Journal bearings 226 react forces from the fin anddihedral lever into yoke 21. Seals 223 maintain a seal between theinternal bore of yoke 21 and the external surfaces of fin carrier 221and also seal against the internal faces (not shown) of fin 3. Afour-point, bearing and seal cartridge 25 retains the turret assembly 21in the propeller hub 101 and is sufficiently dimensioned to take theradial, axial and tilting loads imposed by fin 3 and dihedral leverwithout brinelling under the continuous load fluctuation exerted by fin3.

A dihedral link, 131 comprising a high-capacity plain spherical bearing132 is retained to the inner end of dihedral lever 241 by screw 133.

The root section of fin 3 is yoke-shaped. The fin is assembled bypushing the inner faces of the leading and trailing edge bosses over theprojecting sealing lips of seals 223. Once in position pin 3511 isinserted. Nose cone 353 and end cap 3512 complete with O-rings 354 arethen pushed in either end of the fin bore. Once in position screw 355 isinserted and tightened and plug 3514 with its seal 3515 is inserted.This arrangement provides an exceptionally robust pivot and allows thesimple exchange of individual fins when required.

FIG. 12

FIG. 12 shows a cross axis section through a propeller hub 101 and aturret 20. The turret 20 comprises a yoke 21, a fin carrier 221externally splined to a dihedral lever 241, the splines preferentiallycomprising a master spline 2214, and comprising internal splinespreferentially including a master spine 2213. A dihedral link 13 isspherically jointed to the lower end of the dihedral lever 241. Thelength between axes of the dihedral lever 241 is 2411.

A bearing cassette 25 fitted to an abutment at the lower end of yoke 21is arranged with contact angles such that reaction vectors 2593, 2594intersect the pitch axis AA at 2591, 2592 respectively. The distancebetween these two intersection points is 259. The distance 2595 betweenthe dihedral pivot axis BB and point 2591 and the distance 259 shouldeach be as great as possible to resist the turning moment about thepivot axis BB exerted by the lift and centripetal moment generated byfin 3 and the control moment exerted by the dihedral lever 241.

FIG. 13

FIG. 13 shows a detail section through the pitch bearing cassette 25which preferentially comprises a four-point full-complement bearing 261comprising an upper and a lower seal 2614, a split inner ring and asingle outer ring. The split inner ring is clamped to an abutment ring211 of yoke 21 by a cylindrical seal counterface 2544. Counterface 2544is preferentially manufactured from a hardened stainless steel andcoated by vapour deposition or other suitable method.

Seal 254 preferentially comprising an outer lip 2541 and inner lip 2542and an external static sealing arrangement 2543 is preferentiallytrapped between the outer race of bearing 261 and an abutment 1011formed in the propeller hub 101. Sealing lips 2541, 2542 rotate aboutthe seal counterface 2544.

Bearing 261 is preferentially maintained against an abutment 1012 in thehub by a pressure ring 262.

FIG. 14

FIG. 14 shows a detail of the pitch control mechanism of propeller 1.Turret 20 with its attached fin 3 is free to rotate about the pitch axisAA. A pitch shuttle 443 is free to slide along and pivot about slider4432 which is attached to hub 101 (not shown) of propeller 1. A pitchlink 12 is screwed to an abutment arranged in shuttle 443 andspherically pivoted to pin 211 (not shown) of yoke 21 (not shown). Pitchlink 12 comprises an elastic hinge 1211. The pitch shuttle positionalong axis CC is controlled by an actuator (not shown). Movement of thepitch shuttle along axis CC causes the turret 20 and its attached fin 3to rotate about the pitch axis AA

FIG. 15

FIG. 15 shows a detail of the pitch and dihedral control mechanismsviewed from within the propeller hub 101 (not shown) in which the pitchangle is set to 90 degrees such that the dihedral axis BB is settransversely and the dihedral angle is set to 0 degrees. The pitch angleis defined in this description as the angle between the root chord of afin and the forward direction of axis CC. A dihedral shuttle 453 is freeto slide along axis CC, its position being controlled by an actuator(not shown). Shuttle 453 comprises a plurality of trunnions 4531preferentially equal to the number of turrets 20 fitted to propeller 1(not shown). A dihedral link 13 is spherically pivoted to each of thetrunnions 4531, the other end of which is attached to the inner end ofeach dihedral lever 241. A swing link 14 is preferentially sphericallypivotally attached to the outer end of each of the trunnions 4531 (FIG.15), its other end being spherically pivotally attached to abutmentsarranged internally within pr opener hub 101 (not shown) by means ofscrew 141. Only one such set of links and levers is shown for clarity.

As the dihedral shuttle is moved along axis CC from a zero dihedralangle point P1, the shuttle will be rotated about axis CC by theinfluence of the swing links 14. When swing link 14 is rotated to pointP2 the propulsor 1 will achieve its maximum dihedral angle. As shuttle453 is further displaced under the action of the actuator to the pointwhere fin 3 (not shown) is fully folded, swing link 14 will furtherrotate to point P3.

FIG. 16

FIG. 16 shows a detail of the pitch and dihedral control mechanismsviewed from within the propeller hub 101 (not shown) in which the pitchangle is set to 90 degrees such that the dihedral axis BB is settransversely and the dihedral angle is set to 45 degrees. Preferentiallyfor values higher than 45 degrees the pitch should be maintained at 90degrees and the fin should be considered to be folding rather thanproviding propulsive power.

FIG. 17

FIG. 17 shows a detail of the pitch and dihedral control mechanismsviewed from within the propeller hub 101 (not shown) in which the pitchangle is set to 90 degrees such that the dihedral axis BB is settransversely and the fin is folded.

FIG. 18

FIG. 18 shows a detail of the pitch and dihedral control mechanismsviewed from within the propeller hub 101 (not shown) in which the pitchangle is set to 40 degrees representing approximately the maximumforward pitch state and the dihedral angle is set to 0 degrees.

FIG. 19

FIG. 19 shows a single dimensional force diagram for a case similar tothat shown in FIG. 18, but in which a small dihedral angle has beenadded. In this case the force 13 represents the in-plane force generatedin the dihedral link 13 (FIG. 18), force 241 represents the in-planeforce generated in the axis of the dihedral lever 241 (FIG. 18) and 14represents the in-plane force generated in link 14 (FIG. 18).

The dihedral lever side force has to be reacted by the pitch momentapplied. This is undesirable as it will increase or decrease the pitchmoment. If it increases the pitch moment it will increase the size ofthe pitch actuator and the energy required to control pitch. If itdetracts from the pitch moment it could cause reversal of the pitchmoment causing potential control problems and the potential for thepitch angle to swing to full reverse in case of a failure in the pitchcontrol function. This could result in a catastrophic failure.

It will be evident that by optimising the position in which the swinglink 14 is attached to the propeller hub 101, the direction andmagnitude of the dihedral lever side force can be optimised,particularly over the range of pitch angles where high thrust forces aregenerated.

FIG. 20

FIG. 20 shows a rectangular envelope for the maximum extents of pitchand dihedral angles within a normal working range. A propulsor accordingto the present invention is designed to have a minimum pitch angle of 40degrees, representing the maximum forward drive condition, and a maximumpitch angle of 97 degrees, representing the full reverse condition. Thepropulsor may also be designed for a maximum working range of dihedralangles of 0 degrees to 45 degrees over which the full pitch angle rangeis required. For the range of dihedral angles of between 45 degrees and90 degrees a propulsor may be considered to be folding, with 90 degreesbeing the fully folded condition. During folding it may be necessary tomaintain the pitch angle at 90 degrees to avoid clashed in the pitch anddihedral mechanisms and to maintain the angles of the pivots withintheir design limits.

FIG. 21

FIG. 21 shows a mechanism which is designed to produce the envelopeshape of FIG. 20, in the condition shown fin 3 is in the fully foldedposition and the dihedral lever 241 is fully forward. Pitch is set to 90degrees. In this condition any change in the pitch angle would cause achange in the dihedral angle and would cause severe loading of thedihedral link joints 13.

FIG. 22

FIG. 22 shows the mechanism of FIG. 21 set to the maximum design valueof dihedral of 45 degrees and with pitch set to 90 degrees. In thiscondition the rear spherical joint of the dihedral link 13 is aligned onthe pitch axis AA. Accordingly the pitch angle can be changed as desiredwith no effect on the dihedral angle.

FIG. 23

FIG. 23 shows the mechanism of FIG. 21 set to the minimum design valueof dihedral of 0 degrees and with pitch set to 90 degrees. In thiscondition the forward spherical joint of the dihedral link 13 is alignedon the pitch axis AA. Accordingly the pitch angle can be changed asdesired with no effect on the dihedral angle.

FIG. 24

FIG. 24 shows the mechanism of FIG. 21 set to the maximum design valueof dihedral of 45 degrees and with pitch set to 40 degrees viewed frominside the hub. This drawing shows the rear spherical joint of thedihedral link 13 aligned on the pitch axis AA, enabling the pitch angleto be changed as desired with no effect on the dihedral angle.

FIG. 25

FIG. 25 shows an isometric view under the same conditions as FIG. 21.This view shows the swing link 14 anchored to the propeller hub 101 byscrew 141.

It will be appreciated that the fins, turrets and mechanisms includingbearing arrangements, seals, yokes, links, etc. required for this sortof propeller require to be heavily tooled and produced in high volumesto ensure economic production costs together with high quality standardsand low weight. Accordingly, the object of the current invention is todevise a propeller using a plurality of common components.

A wide variety of marine propellers are normally required to cover anyparticular band of power, boat speed and engine speed and this resultsin a major manufacturing and logistical problem. As a result largerpropellers, in particular, are frequently manufactured to order with aconsequent delivery delay.

Prior art propellers have usually consisted of a fixed number of bladesintegrally manufactured on a hub of cylindrical or swept section

Prior art controllable pitch propellers for marine applications havegenerally been constructed as shown in Duncan (U.S. Pat. No. 6,332,818)FIG. 10( b)

A propeller hub comprises a hub which may accept a number of bladeturrets. The preferred number is between three and six, although inpractice the number may vary from two upwards. This construction allowsa six bladed propeller with common components to absorb approximatelytwice the power of a three bladed propeller with four and five bladedpropellers being able to absorb intermediate power.

This construction also allows a single fin type to be used for apropeller size capable of transmitting between 50% and 100% of itsdesign power with little variation in propulsive efficiency. Asdescribed in Patent Application EP 06120796.5 of equal date, propellerblades may be cut down from some maximum length such that even fineradjustment of the propeller to the power to be transmitted and theperformance required may be achieved.

In this construction the only components which change for the power bandabove are the hub and the pitch and dihedral shuttles. All othercomponents and assemblies are common.

The hub may be manufactured as a casting or moulding from modulartooling.

This approach allows a propeller which is closely matched to the hullperformance and engine characteristics to be made up from a small numberof standard components which can be stocked thus cutting down lead timesfrom weeks or months to hours.

For instance, this construction requires the following part numbers andtools to cover a power band multiplier of 16 (say from 100 hp to 1600hp):

New Application Prior Art RH LH RH LH Forgings & tools (Fins) 5 5Patterns 20 300 300 Total tools 25 5 300 300 Fin part numbers 15 15 Hubmoulds/casting part 4 numb ers Propeller Part numbers 19 15 600 600(Single & Dual propellers including different materials)

FIG. 26

FIG. 26 shows an isometric view of a modular hub 101 for a propellerhaving controllable pitch and/or controllable dihedral, rake, swash ortilt. Hub 101 comprises a forward cooperating casing 1012 and an aftcooperating casing 1011 each comprising recessed engagement means 1015into which fin assemblies (not shown) can be inserted. The twocooperating hub sections are clamped together by through bolts 1013.Plugs 1014 are sealed into the forward casing 1012 to prevent tamperingand corrosion. The forward cooperating casing 1012 comprises pairs ofholes 1061 to enable a bolted connection to a hollow propeller shaft(not shown).

The cooperating casings 1011, 1012 define a hollow interior into whichthe control mechanism for controlling the movement of the fins can beplaced.

FIG. 27

FIG. 27 shows an isometric of a the modular hub of FIG. 38 afterbolting. A single fin and turret assembly 20 is shown fitted in placeduring the bolting process.

FIG. 28

FIG. 28 shows a side view of a six fin propeller 1 comprising a modularhub 101. The propeller is shown with a single fin 3 and turret assembly20 fitted for clarity. The fully assembled propeller comprises 6 fins 3and turret assemblies 20, 6 pitch links 12, dihedral links 13 and swinglinks 14. The pitch links 12 are bolted to a pitch shuttle 443 at oneend and are spherically pivoted to pin 211 of yoke 21 at the other end.The dihedral links 13 are spherically pivoted to a dihedral lever 241 atone end and to trunnion 4531 of a dihedral shuttle 453 at the other. Theswing link 14 is spherically pivoted at one end to the outer end of atrunnion 4541 of the dihedral shuttle 453 and at the other end to a pin141 fixed to the forward hub casing 1012.

FIG. 29

FIG. 29 shows an isometric view of a four fin propeller 1 comprising amodular hub 101, a cover 103, four fins 3 and turret assemblies 20.

FIG. 30

FIG. 30 shows an isometric view of a four fin propeller of FIG. 41 withthe fins 3 in a folded position.

Low Churning Propeller Hub

In particular surface piercing propellers arranged for controllablepitch have been designed with an essentially cylindrical hub of largediameter. Such a hub is claimed in Eriksson EP1280694 (US2003157849).Duncan U.S. Pat. No. 6,332,818 disclosed a large diameter hub with aswept profiled surface.

The hubs of propellers of this Art tend to be wholly or substantiallyimmersed when the hull to which they are fitted is at rest or istravelling at displacement speeds. Under theses conditions it has beenfound that the propeller hub creates substantial churning losses suchthat the power required to overcome said churning losses result in asignificant reduction in propulsive efficiency.

The churning losses are proportional to the following factors:

-   -   (RΩ)²=The square of the speed of any part of any surface in        contact with the water, and,    -   A=The surface area of any surface in contact with the water at a        radius of R from the rotational axis, and,    -   Cd_(f)=the friction drag coefficient of any surface A in contact        with the water, and,    -   Cd=the drag coefficient due to the form of any surface A in        contact with the water.

The total churning power (P_(c)) is given by the expression below:

Pc=Σ(R×Ω×(R×Ω)² ×A×(Cd _(f) +Cd))=Σ(R ³×Ω³ ×A×(Cd _(f) +Cd))

From which it is evident that to minimise churning and the consequentpower loss during low-speed operation the following requirements shouldbe met:

-   -   The rotational speed Ω should be kept as low as possible, and,    -   The area A of any surface in contact with the water should be        kept as low as possible and the radius R at which any such        surface area is arranged from the axis of rotation should be        minimised, and,    -   The form drag coefficient Cd and the friction drag coefficient        Cd_(f) should be kept as low as possible.

FIG. 31

FIG. 31 shows the rear view of a craft fitted with dual propulsors 1each with three fins 3. The craft is travelling at sufficient speed forthe transom cavity to be fully developed. Thus the hubs 101, turrets 20and the roots of fins 3 operating in the transom cavity such that theyare not immersed. At lower speeds the hubs and turrets would beimmersed. Although the diameter of the hubs 101 is small and theyconsequently would not add very significantly to the churning losses,the turrets 20 have a relatively large diameter and a bluff form. Theirmean square radius is also significantly larger and the churning lossesgenerated by such a form would be high.

FIG. 32

FIG. 32 shows a rear view of an improved hub 101 for a surface-piercingpropeller 1 having a broadly polygonal shape at larger swept diametersblending into a generally swept surface at smaller radii. The polygonalsurfaces create partial cavities as they rotate such that only a smallpart of the surface of the propeller hub is in contact with the water.As a consequence the churning losses generated by this improved hub formare much improved. The root sections of the fins 3 blend into the turretprofiles. Due to their generally smooth form they generate only modestchurning and the losses are further reduced by the fact that they do notcreate a continuous ring such that each will tend to operate in thecavity created by its predecessors.

FIG. 33

FIG. 33 shows a side view of the improved hub of FIG. 31 from which itis evident that the root sections of fins 3 and the profiles of turrets20 present a small cross sectional area of non-continuous section.

FIG. 34

FIG. 34 shows a view from the rear of a modular hub 101 illustrated witha single turret 20 in position. The forward cooperating casing 1012 isillustrated with pairs of holes 1061 corresponding to the number ofturrets 20 for which the hub is designed to enable a bolted connectionto a hollow propeller shaft (not shown). The hub illustrated is designedfor 6 turrets whereas a hub designed for 5 turrets may comprise 5 pairsof fixing holes 106 1.

FIG. 35

FIG. 35 shows a rear view of a propeller shaft 501 which had a series oftapped holes allowing 3, 4, 5, or 6 fin propellers to be fitted to ashaft.

FIG. 36

FIG. 36 shows a front view of a propeller 1 comprising four fins 3, eachof which may be raked about an axis BB in the plane of the propeller andpitched about an axis AA. The propeller tips rotate through circle 151,the propeller roots rotate through circle 152. Fins 3 are pitched at anangle of 45 degrees about axis AA and raked by angle of 30 degrees aboutaxis BB

It will be noted that at both the tip and the root sections of fins 3the leading and trailing edges describe different circles as they rotateabout axis CC. This means that the flow through the propeller at anyparticular point does not follow a design section.

This has a number major disadvantages:

-   -   Due to the twist along the span of a fin as shown in FIG. 10,        the curvature of the fin section seen by the flow will be less        curved or more curved depending on whether the rake angle is        more or less than the design figure.    -   An increase in curvature results in an increased lift        coefficient as shown in FIG. 82. This in turn means that        maintaining the correct torque requirement will require that the        pitch is reduced which may result in the leading edge operating        at negative incidence which would tend to swap the cavity to the        other side of the fin. This would result in an unstable flow        pattern and could cause hunting of the propulsion controls or        the engine controller or both.    -   A decrease in curvature would result in a reduction in the lift        coefficient which would require an increase in the leading edge        incidence. However, this might not be sufficient to prevent the        flow breaking away near the trailing edge, this could result in        local cavitation.

Additionally, it will be clear from looking at the drawing that the flowaround the root and tip sections would be perturbed. This would resultin a significant loss of performance.

FIG. 37

FIG. 37 is an isometric view the propeller of FIG. 36.

FIG. 38

FIG. 38 shows the propeller of FIG. 36 operating at 0 degrees of Rakeand 9 0 degrees of pitch. If the propeller and fins are designed for 0degrees of rake the un-raked propeller operates normally.

FIG. 39

FIG. 39 is an isometric view the propeller of FIG. 38.

FIG. 40

FIG. 40 shows a front view of a propeller 1 comprising four fins 3, thedihedral angle of which may be varied about an axis BB generallyparallel to the root of each fin. The pitch of each fin may be varied byrotation about an axis AA. The propeller tips rotate through circle 151,the propeller roots rotate through circle 152. Fins 3 are pitched at anangle of 45 degrees about axis AA and given a dihedral angle of 30degrees about axis BB

It will be evident from this drawing that unlike in the case of rake theboth the leading and the trailing edges of the fins sweep closely aroundcircle 151 at the tip and circle 152 at the root. This results in theflow at any radius following a design section such that there are nosignificant additional losses.

FIG. 41

FIG. 41 is an isometric view the propeller of FIG. 40

FIG. 42

FIG. 42 shows a front view of a propeller 1 with the same configurationas that of FIGS. 40 and 41. Fins 3 are pitched at an angle of 90 degreesabout axis AA and given a dihedral angle of 0 degrees about axis BB

As for the propeller of FIG. 40 the flow remains aligned with the designsections.

FIG. 43

FIG. 43 is an isometric view the propeller of FIG. 42

FIG. 44

FIG. 44 shows a front view of a propeller 1 comprising four fins 3, theswash angle of the propeller may be varied about an axis BB which passesthrough the axis CC and is normal to said axis. The pitch of each finmay be varied by rotation about an axis AA. The propeller tips rotatethrough circle 151, the propeller roots rotate through circle 152. Fins3 are pitched at an angle of 90 degrees about axis AA and the propellerhas a swash angle of 0 degrees about axis BB

It will be evident from this drawing that both the leading and thetrailing edges of the fins sweep closely around circle 151 at the tipand circle 152 at the root. This results in the flow at any radiusfollowing a design section such that there are no significant additionallosses.

FIG. 45

FIG. 45 is an isometric view the propeller of FIG. 44

FIG. 46

FIG. 46 shows a front view of a propeller 1 of the same configuration asFIG. 44. The propeller tips rotate through circle 151, the propellerroots rotate through circle 152. Fins 3 are pitched at an angle of 45degrees about axis AA and the propeller has a swash angle of 30 degreesabout ax is BB

It will be evident from this drawing that both the leading and thetrailing edges of the fins do not sweep closely around circle 151 at thetip and circle 152 at the root, other than when the fins are alignedwith axis BB. Not only do the fins become angled to the flow under otherconditions, but they sweep an elliptical trajectory. This results in theflow at any radius failing to follow a design section such that therewill be significant additional losses.

FIG. 47

FIG. 47 is an isometric view the propeller of FIG. 46

FIG. 48

FIG. 48 shows a side view of a propeller 1 of the same configuration asFIG. 46 from which it will be evident that there will be a largedifference in the pitch angle as the propeller rotates. This would havea very negative influence on performance.

FIG. 83 shows incidence changes up to 15 degrees resulting in a changeof lift coefficient of 400%. FIG. 82 shows a corresponding reduction inthe lift/drag ratio to just 22% of its design value, at 30 degrees ofswash angle the variation in pitch from one side to the other would be+/−30 degrees. The resulting large thrust reversal from side to sidewould result in a very large performance loss, high levels of vibrationand a large moment on the craft.

The combined effects shown in FIGS. 46 and 48 make this an unacceptableoption.

FIG. 49

FIG. 49 shows a front view of a propeller 1 comprising four fins 3, thetilt angle of the propeller may be varied about an axis BB normal toaxis CC, the axis of rotation of the propeller (see FIG. 67). The pitchof each fin may be varied by rotation about an axis AA. The propellertips rotate through circle 151, the propeller roots rotate throughcircle 152. Fins 3 are pitched at an angle of 90 degrees about axis AAand the propeller has a swash angle of 0 degrees about axis BB

It will be evident from this drawing that both the leading and thetrailing edges of the fins sweep closely around circle 151 at the tipand circle 152 at the root. This results in the flow at any radiusfollowing a design section such that there are no significant additionallosses.

FIG. 50

FIG. 50 is an isometric view the propeller of FIG. 49.

FIG. 51

FIG. 51 shows a front view of a propeller 1 of the same configuration asFIG. 49. The propeller tips should ideally rotate through circle 151,the propeller roots should ideally rotate through circle 152. Fins 3 arepitched at an angle of 45 degrees about axis M and the propeller has atilt angle of 30 degrees about axis BB

It will be evident from this drawing that the both the leading and thetrailing edges of the fins do not sweep closely around circle 151 at thetip and circle 151 at the root, other than when the fins are alignedwith axis BB. Not only do the fins become angled to the flow under otherconditions, but they sweep an elliptical trajectory. This results in theflow at any radius failing to follow a design section such that therewill be significant additional losses.

FIG. 52

FIG. 52 is an isometric view the propeller of FIG. 51

FIG. 53

FIG. 53 shows a side view of a propeller 1 of the same configuration asFIG. 51 from which it will be evident that there will be a largedifference in the pitch angle as the propeller rotates. This would havea very negative influence on performance. FIG. 83 shows incidencechanges up to 15 degrees resulting in a change of lift coefficient of400%. FIG. 82 shows a corresponding reduction in the lift/drag ratio tojust 22% of its design value, At 30 degrees of tilt angle the variationin pitch from one side to the other would be +/−30 degrees. Theresulting large th rust reversal from side to side would result in avery large performance loss, high levels of vibration and a large momenton the craft.

The combined effects shown in FIGS. 65 and 67 make this an unacceptableoption.

FIG. 54

FIG. 54 shows a control block schematic to change port and starboardpitch and engine speed in response to the pilot's movement of theahead/astern variable control and a helm, and in response to craft roll,pitch and yaw rate sensors or from appropriate signals from an inertialmeasurement unit or an inertial navigation system.

In this embodiment the engine load is constrained to values determinedby the engine speed set points or the actual engine speeds.

FIG. 55

FIG. 55 shows a control block schematic to control the port andstarboard dihedral angle according to the errors in boat running trimand the motion of the craft in yaw, pitch and roll.

FIG. 56

FIG. 56 is a control block schematic to output signals to the pitch anddihedral controllers based on craft motion determined by an Inertialmeasurement unit or an inertial navigation system

FIG. 57

FIG. 57 shows a ghosted partial hull prepared for the installation ofdual engine s and propulsors. On either side of the hull a pair of frontmounts 810 are attached to stringers 601 forming part of the hullstructure 6, and a rear mount 61 is attached to a transom 604 alsoforming part of said hull structure. The front mounts 810 are arrangedto take axial and lateral loads in addition to vertical loads. The rearmounts 61 are arranged predominantly to take vertical and lateral loadsand to be compliant in the axial sense.

It will be evident that additional sets of front and rear mounts couldbe positioned to accommodate additional engine/propulsor units.

FIG. 58

FIG. 58 shows a ghosted partial hull prepared for the installation of asingle engine/dual propulsor unit. A pair of front mounts 810 areattached to stringers 601 on either side of the hull forming part of thehull structure 6, and a rear mounts 61 are attached to a transom 604also forming part of said hull structure.

FIG. 59

FIG. 59 shows a typical load deflection curve for vertical or lateraldeflections for a preferred rear mount. The load taken by such a mountin the axial direction is preferentially a maximum of 20% of thevertical or lateral load for the same deflection.

The mount will preferentially be designed for a static deflection in therange of 3.5 mm to 5.5 mm shown at point X and to have a quasi linearload deflection characteristic around this point. As the load increasesbeyond point Y, the rate increases progressively.

In the opposite sense, the load decreases quasi linearly initially andthen starts to decrease rapidly as the deflection decreases further.This situation corresponds to unloading the mount due to lifting forcesgenerated by the propulsor or by negative acceleration in rough seaconditions.

In an optional design the rate curve is designed to be mirrored aboutpoint X to provide close control of the propulsor position whilstproviding the required noise and vibration isolation.

FIG. 60

FIG. 60 shows a section through a preferred rear mount in the zy planeunder static loading only. A transom mount assembly 61 is fitted to thetransom 604 of a craft whereby a transom plate 611 is clamped by counterplate 613 by means of a number of fixing bolts 614 which pass throughjig-drilled holes in transom 604 of a craft. A compliant formed seal 612ensures a static seal between the transom plate 611 and the transom 604.

A resilient moulding 831, preferentially manufactured from amicro-cellular polyurethane material is inserted into an outer housing832 and pushed onto the aft gear casing 512 to which a retainer 837 hasbeen loosely placed. Prior to pushing the resilient moulding 831 ontothe gearcasing 512 its interior profile is substantially smaller thanthe corresponding profile of the gearcase. The act of pushing themoulding into position creates a substantial pre-compression of themount which ensures that suffient sealing pressure is maintained betweenthe resilient moulding 831 and both the outer housing 832 and thegearcasing 512 under all conditions. A plastic ring 5121 (see FIG. 61)is preferentially bonded onto the end of the aft gearcasing 512 toprevent corrosion.

The gearcasing 512 together with its associated propeller shaft 501,rear propeller shaft bearing 502 and shaft seal 110 and with retainer837, outer housing 832 and resilient moulding 831 is inserted frominboard the craft (right-hand side of the drawing) and is retained inposition by retainer 837 which is fixed by a number of bolts 836.

The outer housing 832 is preferentially ring-shaped and manufacturedfrom a water resistant reinforced plastic material. A eccentric form isindicated in the drawing but the requirement for this will depend on thespecific shape of the mating components.

The transom plate 611 is preferentially manufactured from a plasticmaterial.

The resilient moulding 831 is preferentially annular in form.

FIG. 61

FIG. 61 shows a partial detail of the section through the rear mountshown in FIG. 60 also under static loading only.

The outer housing 832 preferentially has a forward internal lip 8321 anda rear internal lip 832 which serve to prevent the resilient mount fromsliding due to axial forces, especially once it has been pre-compressed.It also comprises an external O-ring and groove 834 or other means ofensuring a static seal between it and the transom plate 611

The aft gearcase preferentially comprises a swept profile 5122 whichprevents the resilient mount from sliding along it in the pre-compressedstate.

In the static loaded condition there should preferentially be a smallradial gap between the nose 8311 of the resilient mount 831 and theinternal profile of retainer 837 as shown. This gap may vary around theperiphery of the nose piece, but should preferentially be adjusted to1.0 mm and 3.0 mm in the static laden condition. This is generallysufficient to ensure an adequate range for the desired linearload/deflection curve about point X of FIG. 59. By maintaining such agap the rate of the mount at this condition will be determined by theradially thicker main body of the mount 8312, wherein ‘rate’ is taken tomean the local slope of the load/deflection curve at load applied to themount. Maintaining a constant radial clearance in this condition willgive the mount a characteristic similar to the optional load-deflectioncurve of FIG. 103, whereas increasing the radial gap towards the top ofthe mount will provide a characteristic similar to the Force/Deflectioncurve of FIG. 59.

It will be evident to those skilled in the Art that the load/deflectioncurve of mount 832 will be approximately equal to the sum of the curvesdue to the main body and the nose of the mount in isolation and that byadjusting the radial thicknesses and axial lengths of the two parts, byadjusting the preload in the main body of the mount, and by variation ofthe compound from which the mount is manufactured as well as itsdensity, the mount may be tuned to the desired characteristics. It willalso be evident that as the material is in shear in the axial direction,its rate will be substantially lower than in the radial sense where thematerial is in compression.

FIG. 62

FIG. 62 shows a resilient mount with an alternative form with acircumferential groove 8313 moulded in it. As the mount is radiallydeflected this has much the same effect as the nose piece 8311contacting the inner profile of retainer 837. This alternativearrangement also comprises an internal ring 833 which is sealed to theaft gear case 512 by an O-ring 834 and which comprises a V-clamp 835 toretain it to the aft gear case.

This alternative arrangement can simplify assembly of the aft gearcasing into the mount.

FIG. 63

FIG. 63 shows a side view of a unitary propulsion package comprising apropeller 1, close-coupled to a gearbox 5 and an engine 8. The unit ismounted to the hull stringers 601 (see FIG. 58) on two front mounts 81and to the transom 604 (see FIG. 58) by a rear mount 83. The engine ispreferentially fitted with a ladder frame or structural sump 82.

The displacement curve in this figure shows a desirable deflection curvefor the first order modal frequency of the complete unit about someneutral axis. The front and rear mounts are preferentially arranged suchthat they are subject to little or no deflection at this frequency.

In practice, the precise deflection curve may vary due to tolerancevariations, changes in fluid levels in the engine and gearbox, thenumber of fins fitted to the propulsor, etc. As a consequence it willnot be possible to ensure that the mounting positions are ideally placedunder all conditions and it is generally sufficient that they are placedwithin +/−10% of the total length L, although the acceptable rangevaries depending on the proximity of forcing frequencies to the firstorder modal frequency in bending of the complete propulsion unit

Although the resonance is shown in the vertical longitudinal plane forconvenience, it is unlikely to be precisely in this plane due tounsymmetry.

Whilst the propulsion unit is shown comprising an internal combustionengine it will be clear to those skilled in, the Art that any other formof prime mover such as an electric motor, gas or steam turbine, etc. maybe fitted.

FIG. 64

FIG. 64 shows a top view of a unitary propulsion package comprising apropeller 1, close-coupled to a gearbox 5 and an engine 8. The unit ismounted to the hull stringers 601 (not shown) on two front mounts 81(not shown) and to the transom 604 (not shown) by a rear mount 83. Theengine is preferentially fitted with a ladder frame or structural sump82 (not shown).

The displacement curve in this figure shows a desirable deflection curvefor the first order modal frequency of the complete, unit about someneutral axis. The front and rear mounts are preferentially arranged suchthat they are subject to little or no deflection at this frequency.

In practice, the precise deflection curve may vary due to tolerancevariations, changes in fluid levels in the engine and gearbox, thenumber of fins fitted to the propulsor, etc. As a consequence it willnot be possible to ensure that the mounting positions are ideally placedunder all conditions and it is generally sufficient that they are placedwithin +/−10% of the total length L, although the acceptable rangevaries depending on the proximity of forcing frequencies to the firstorder modal frequency in bending of the complete propulsion unit

Although the resonance is shown in the Horizontal longitudinal plane forconvenience, it is unlikely to be precisely in this plane due tounsymmetry.

It is likely that the modal frequency in this plane is at a lowerfrequency than that in the essentially vertical plane due to differencesin stiffness. Accordingly this mode of vibration may be the morecritical.

Whilst the propulsion unit is shown comprising an internal combustionengine it will be clear to those skilled in the Art that any other formof prime mover such as an electric motor, gas or steam turbine, etc. maybe fitted.

FIG. 65

FIG. 65 shows a side view of a separate propulsion package comprising apropeller 1, close-coupled to a gearbox 5 and a remote-mounted engine 8.A structurally stiff frame 86 is mounted to the front end of thegearcase. The unit is mounted to the hull stringers 601 (not shown) ontwo front mounts 81 and to the transom 604 (not shown) by a rear mount83.

The engine is remote mounted. A drive shaft 861 connects the engineflywheel to the gearbox input shaft. The drive shaft is preferentiallymanufactured from carbon fibre to achieve the required torsionalstiffness to avoid vibration. A torsionally flexible coupling (notshown) may be fitted either at the engine end or the gearbox end of thedrive shaft.

The same vibration and mounting criteria apply for the separatelymounted unit as shown.

Whilst the propulsion unit is shown comprising an internal combustionengine it will be clear to those skilled in the Art that any other formof prime mover such as an electric motor, gas or steam turbine, etc. maybe fitted.

FIG. 66

FIG. 66 shows a typical cyclical thrust and torque characteristics for a5 bladed propulsor. In general the cyclical variation reduces withincreasing number of blades

FIG. 67

FIG. 67 shows a Fourier Analysis for the thrust curve of FIG. 66 showingthat although the first and second order blade frequencies (5 ^(th) and10^(th) order propeller frequencies) are dominant, the amplitude ofhigher orders is still significant.

FIG. 68

FIG. 68 shows the cyclical thrust variation for the first and secondorder blade frequencies (5^(th) and 10^(th) order propeller frequencies)plotted against the actual cyclical thrust variation. It is clear fromthis graph that although the magnitude variation is significant, theenergy variation represented by the difference in area under the curvesis much smaller. This indicates that isolation against these two orderswill result in a low vibration system at least for 5 or 6 bladepropellers.

Similar curves for 3 and 4 blade propellers, show that it becomesincreasingly necessary to isolate against third order blade frequencies(15^(th) order propeller frequencies) to achieve desirable noise andvibration isolation.

FIG. 69

FIG. 69 shows typical transmission factors for first and second orderblade frequencies (6^(th) and 12^(th) order propeller frequencies) for a6 bladed propulsion system designed for a maximum engine speed of 4,000rpm. Although a transmission factor of above 2 is indicated this hasbeen found to result in acceptable levels of noise and vibrationprovided the mounts are arranged as in FIGS. 63 to 65.

FIG. 70

FIG. 70 shows typical transmission factors for first order bladefrequencies (3^(rd) order propeller frequencies) for a 3 bladedpropulsion system designed for a minimum engine speed of 800 rpm. Thisresults in very adequate levels of vibration at low idle speeds andabove.

FIG. 71

FIG. 71 shows typical transmission factors after attenuation through themounts for second order blade frequencies (12^(th) order propellerfrequencies) for a 6 bladed propulsion system designed for a range ofengine speed from 800 rpm to 4,000 rpm. A relatively low transmissionfactor 0.2 is indicated and this has been found to result in acceptablelevels of noise and vibration provided the mounts are arranged as inFIGS. 63 to 65.

FIG. 72

FIG. 72 shows the drive train between the engine flywheel 801 and thepropeller 1 in which 803 is a optionally a drive coupling or atorsionally resilient coupling, 804 is a drive shaft, 532 is a gearboxinput shaft, 534 is a pinion gear, 544 is an output gear and 501 is apropeller shaft. The engine flywheel is preferentially a dual massflywheel. In cases where 801 is a rigid flywheel 803 must comprise atorsionally flexible coupling

FIG. 73

FIG. 73 shows an isometric underside view from the front of a hull 6fitted with a 6 bladed surface-piercing propeller 1. The hull comprisesa flow guide 63, preferably of arcuate profile axially aligned withpropeller 1 so as to guide the water flow around the propeller. Thewater flow separates at the aft end 631 of the flow guide such that thehub 101, the roots of fins 3 and the turrets 20 rotate within saidcavity.

The hull 6 preferentially comprises a combined platform and propellershroud which comprises a vent (not shown) with a rear opening and twointernal openings arranged in the arcuate surfaces forming protectiveshrouds around the propellers 1.

FIG. 74

FIG. 74 shows the rear view of a hull 6 fitted with a six-bladedsurface-piercing propeller 1. The hull has an under surface 605.

The root blend profile 305 of each fin 3 sweeps a circle 152 whichshould remain within the rear profile 631 of the flow guide 63 of FIG.73 to avoid undesirable thrashing losses.

FIG. 75

FIG. 75 shows an isometric view of a unitary single engine propulsionpackage comprising two propellers 1 (not shown), close-coupled to agearbox 5 and an engine B. The unit is mounted to the hull stringers 601(not shown) on two front mounts 81 and to the transom 604 (not shown) bytwo rear mounts 83. The engine is preferentially fitted with a ladderframe or structural sump 82 (not shown).

FIG. 76

FIG. 76 shows a sectional view of a turret assembly 2 0 arranged forvariable rake comprising a fin carrier 270 for mounting a fin 3 (notshown) comprising a fir-tree root (not shown), The fin carrier isspherically jointed in a spherical cup 276 forming part of the yoke 203.The fin is raked by axial movement of the rake lever 290. Axial movementof lever 271 allows the fin to be controlled in pitch.

FIGS. 77 to 81

FIGS. 77 and 78 show a section through a propeller designed for cyclicalpitch control and cyclical rake and/or dihedral control.

Fins 3 are spherically jointed into blade carrier assemblies 2 of a hub4 which is integrally formed with a hollow propeller shaft 9. Anon-rotating actuator assembly 30 comprises six pistons 32, the positionof which is determined by position sensors 31 connected by cables 311 toan electronic controller (not shown). A non-rotating guide shaft 50 hasa centralising guide bearing 121 in a hub cover plate 12.

Inboard shuttle 5 and outboard shuttle 6 are spherically pivoted tosegmental slider bearings 51 which are free to slide along shaft 50.Shuttles 5 and 6 each comprise non-rotating inner ring elements 502, 602and rotating outer ring elements 501, 601, respectively.

The inner and outer ring elements each comprise angular contact bearingtracks 503 and 603 which enable the rotating outer ring elements torotate around the inner ring elements. These bearings are arranged totake both thrust and journal loads.

A first set of three actuator pistons 32 a are spherically attached tothe non-rotating inner element 502 of the inboard shuttle 5 and a secondset of three actuator pistons 32 b are spherically attached to thenon-rotating inner element 602 of the outboard shuttle 6. The actuatorpistons are connected to the non-rotating inner elements 502, 602 bymeans of rods 33 a and 33 b, each comprising a spherical end 331 whichare connected to spherical sockets in slippers 52 which are slideablyattached to the non-rotating inner elements 502, 602.

An inwardly extending lever 14 (FIG. 80) is integrally mounted to eachfin 3. The inner end of lever 14 is bifurcated terminating in spheres151, 152 which are snapped into slippers 70 slidably attached to theouter rotating elements of the inboard and outboard shuttles 5, 6.Spheres 151 are all connected to the inboard shuttle 5 and the spheres152 are all connected to the outboard shuttle 6. The sliding slipperarrangement could be replaced by spherically pivoted links.

As shown in FIG. 80 each ball 151 and 152 is connected by rigid means 14to a fin such that movement of the inboard shuttle 5 and outboardshuttles 6 causes the fin 3 to move.

There is an axial datum position along the shaft 50 where the innershuttle 5 and the outer shuttle 6 are positioned such that the pitch ofeach fin is ninety degrees and the rake of each fin is zero degrees.

By displacing the first and second set of actuator pistons 32 a and 32 bto the same extent along the shaft 50 in the same axial direction, thefins 3 will be pivoted fore or aft to change the rake angle be cause thefin is caused to pivot in the blade carrier assembly 2, which is locatedat a fixed radial distance from the shaft 50.

By displacing the inboard shuttle 5 and the outboard shuttle 6 inopposite directions away from the datum position and by the same amount,the pitch of each fin will be changed collectively.

In one example, where the outboard shuttle 6 and the inboard shuttle 5are displaced along the shaft 50 away from the axial datum position anddisplaced relative to each other, the dihedral of each fin will bechanged collectively.

By extending the pistons attached to the outboard shuttle 6 and thepistons attached to the inboard shuttle 5 to a varying degree, shuttles5 and 6 can be pivoted relative to the shaft 50 providing independentamounts of cyclical motion as shown in FIGS. 79 to 81. This can be usedto provide cyclical motion to the pitch and dihedral.

FIG. 82

FIG. 82 shows the lift/drag variation against angle of incidence for atypical high-performance ventilating section.

FIG. 83

FIG. 83 shows the lift coefficient variation against angle of incidencefor a typical high-performance ventilating section.

1. A fin for use on a propeller, the fin comprising: a lift generatingsection having a leading edge and a trailing edge, and a pair ofsurfaces extending between the leading and the trailing edges therebydefining a tip and a root having a root chord; and a dihedral sectionintegrally formed with the root of the lift generating section andhaving a rotation axis about which, in use, the lift generating systemcan be rotated to vary the dihedral of the fin, the axis being generallyparallel to the root chord of the lift generating section.
 2. A finaccording to claim 1, wherein the axis of dihedral rotation is within a15 degrees deviation from the root chord.
 3. A fin according to claim 2,wherein the axis of dihedral rotation deviates by no more than 3 degreesfrom the root chord.
 4. A fin according to claim 3, wherein the axis ofdihedral rotation is parallel to the root chord.
 5. A fin according toclaim 1, wherein the dihedral section comprises a front boss adjacentthe leading edge and a rear boss adjacent the trailing edge.
 6. A finaccording to claim 5, wherein each boss is provided with a through holewhich is splined for engagement with a corresponding spline on a shaft,in use.
 7. A fin according to claim 6, wherein the axis of rotationpasses through the centres of the through holes in each boss.
 8. A finaccording to claim 1, wherein the front boss blends smoothly into theleading edge such that no re-entrant form is created between the bossand the leading edge.
 9. A fin according to claim 1, wherein the fin hasa pitch axis and a stack axis, wherein the stack axis is offset from thepitch axis.
 10. A fin according to claim 9, wherein the pitch axis iscloser than the stack axis to the leading edge.
 11. A fin according toclaim 9, wherein the stack axis does not pass through the axis ofrotation.
 12. A fin according to claim 9, wherein the stack axis isangled relative to the pitch axis.
 13. A fin according to claim 1,wherein the centre of pressure of a fin is located forward of the pitchaxis.
 14. A fin according to claim 1, further comprising a stop elementmounted on either or both of the front and rear bosses for limitingrotation of the fin about the axis of rotation in at least onedirection.
 15. A fin according to claim 1, wherein the surface betweenthe front and rear bosses at the root of the fin is shaped such that,when the fin is mounted on a yoke, the surface at the root of the finacts, during rotation, to remove marine growth, sediment or otherunwanted material from the yoke.